The disclosed device relates generally to anchoring devices and fasteners which are utilized to attach adjacent panel members or to attach structures to panel members. It is to be understood that the term “workpiece” as used in this specification refers to any material for which it is desirable to use any of the disclosed embodiments of this device. Typically, but not necessarily, the materials for which such devices have the greatest utility are for thin walled materials such as sheet metal or laminated composite materials, such as carbon fiber and plastic panels, where the matrix material is not conducive for threading or retaining threaded inserts.
It is desirable in some applications, such as utilization with aircraft panels, that the fasteners remain attached to the panel, even after the threads are backed out of the female threads of the structure on the other side of the panel, where the structure may be a nut or other structure having female threads for receiving the fastener. It is known to use various means for retaining the fastener to the panel, such as grommets or clips, such as that shown in FIG. 1. This type of fastener utilizes prongs on the washer which provides proper orientation during installation and removal, and helps to eliminate wear and elongation of the fastener holes in the metallic or composite panels. With the type of device 100 shown in FIG. 1, slots 12 are manufactured along the long axis of the fastener by electrical discharge manufacturing (EDM).
The type of apparatus shown in FIG. 1, and the other prior art devices have some disadvantages. Installing grommets or clips can require additional tooling, and can be time consuming. The most common method, using grommets, requires that the fastener have EDM slots on the side of the fastener, including the portion of the fastener which is preloaded by making the fastener up into female threads. Thus, the EDM slots cause a reduced load-bearing diameter, thus reducing the allowable tensile and shear loads for the fasteners.